[BUG] Co-work Windows: sandbox environment leaks into child processes, breaking Unix domain socket IPC (JVM NIO, Gradle, MCP servers affected)

Found 1 possible duplicate issue:

1. https://github.com/anthropics/claude-code/issues/41432

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Hi, any update?

Same issue for me

I have figured it out, sharing my workaround (I use gitbash for windows):

Heads-up: Gradle / any JVM tool fails in Claude Code on Windows with "Unable to establish loopback connection"

What you'll see

Running Gradle (or any Java command) from Claude Code's terminal on Windows fails with:

java.io.IOException: Unable to establish loopback connection
Caused by: java.net.SocketException: Invalid argument: connect
at sun.nio.ch.UnixDomainSockets.connect0(Native Method)
Same command works fine in your normal PowerShell/Git Bash terminal. Sandbox exclusions don't help

Cause

JDK 17+ on Windows uses WEPollSelectorImpl, which opens an AF_UNIX socket for its internal wakeup pipe. The socket path is built from %TEMP%. Windows' AF_UNIX (and POSIX in general) caps sockaddr_un.sun_path at 108 bytes.

In a normal terminal %TEMP% resolves cleanly (C:\Users\<you>\AppData\Local\Temp\...) and fits. Inside Claude Code's Cowork VM sandbox, the path gets resolved through the overlay filesystem, which prepends an internal prefix — pushing the final path past 108 bytes. The kernel returns EINVAL, every JVM in the sandbox dies on startup. Not fixed in JDK 21 or 25; the limit is an OS-level kernel ABI, not a JVM-tunable.

Related: claude-code#41432.

Fix

Point TEMP/TMP at a short path. In ~/.claude/settings.json:

{
  "env": {
    "JS_CLAUDE": 1
  },
  "sandbox": {
    "filesystem": {
      "allowWrite": ["C:\\jtmp"]
    }
  }
}

Next, in your ~/.bashrc file add:

if [ -n "$JS_CLAUDE" ]; then
  # Runs only when bash is invoked by Claude Code
  export TMP=C:\\jtmp
  export TEMP=C:\\jtmp
fi

Note: you can't set TMP and TEMP env variables in your claude settings, because they're overriden by your system. bashrc loads last.

Then mkdir C:\jtmp and restart Claude Code. Gradle, Maven, plain java — all work again.

Hi, I see the issue is closed. Did you managed to shorten the temp path somehow? I know workaround, but it would be nice to fix it for all users, so they don't have to google it :)

This is very much NOT fixed!

There is a workaround, but the issue itself is not fixed

THANK YOU @jsamczuk , my tycho builds wouldn't run using Claude Code mode in Claude Desktop, same error and same root cause. Your workaround worked and I don't think I would've figured that out on my own.

I also hope that this gets fixed in the desktop client itself, it's a pity this issue got closed without an actual fix in the tool itself.